ESDU STRUCT 01.01.01
The strength of struts.
Abstract:ESDU Struct 01.01.01 provides theoretically derived curves that treat the overall (flexural) buckling of struts in which the cross-section translates normal to the strut axis; the data include the effects of plasticity, load offset and initial bow. Plasticity is taken into account by representing the stress-strain curve of the material by the expressions given in ESDU 76016, which require a material characteristic, m, and the stress, f, at which the tangent modulus is half the elastic modulus of the material in compression. Offset and bow are treated as an eccentricity and if manufacturing tolerances are known their influence is included by increasing the bow; if the tolerances are unknown a formula is recommended from which a value may be calculated. The curves plot the ratio of the average stress in the strut to f against a parameter defined by the product of two ratios: the ratio of the equivalent length of the strut to the radius of gyration of the strut section and the root of the ratio of the maximum allowable stress in the most compressed fibre to f. The equivalent length depends on the end conditions and a table gives values for five cases that include situations in which the conditions differ between the two ends. It may be different in different planes and the minimum is required here. Determination of the radius of gyration when the strut is attached to a skin is discussed. There are four sets of curves, each set relating to a value of the ratio of the eccentricity to a length parameter. That length parameter is defined as the section radius of gyration squared divided by distance from the strut axis to the most compressed fibre. Within each set of curves there are also four sets each relating to a value of m. A worked example illustrates the use of the method. ESDU 90002 introduces a program that treats the cases covered by ESDU Struct 01.01.01 and also local and inter-rivet buckling. That program also allows the case when the bow and offset act in opposition to be calculated, while the method here requires they should act together to increase the bending moment in the centre of the strut.
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